Abstract: To investigate the effects of intratracheal instillation of PM_2.5 suspension on bleomycin (BLM)-induced pulmonary fibrosis in mice and the intervention of neotuberostemonine (NTS), the BLM dose (1.5 or 3.0 U/kg) and PM_2.5 frequency (1 or 2 times per week) were studied by factorial experiment design. After intratracheal instillation of BLM (1.5 or 3.0 U/kg) on day 0, PM_2.5 (5 mg/kg) was intratracheally injected to mice once or twice a week from day 1 to day 21, and the mice in the treatment group were given 30 mg/kg NTS by gavage once a day from day 8 to day 21. The degree of pulmonary fibrosis was evaluated by lung coefficient, hydroxyproline (HYP) content, HE staining and Masson staining lung sections as well as their semi-quantitative index (HE inflammatory score and collagen volume fraction, CVF). The results showed that the HE scores increased significantly in mice singly given PM_2.5 once a week, the HYP content and HE score increased in mice singly given PM_2.5 twice a week, but their CVF values did not significantly increase. However, the CVF values increased significantly in mice treated with PM_2.5 and BLM co-infusion. These results suggested that PM_2.5 (administered singly) could significantly increase BLM-induced collagen deposition and greatly aggravate pulmonary fibrosis although it mainly caused pulmonary inflammation rather than pulmonary fibrosis. NTS could significantly reduce the CVF value and α-SMA protein level of the model mice. It can be concluded that PM_2.5 has great influence on patients with respiratory diseases, while NTS can improve pulmonary fibrosis induced by the combination of PM_2.5 and BLM.